No evidence for effects of infection with the amphibian chytrid fungus on populations of yellow-bellied toads

Abstract

The parasitic chytrid fungus Batrachochytrium dendrobatidis (Bd ) can cause the lethal disease chytridiomycosis in amphibians and therefore may play a role in population declines. The yellow-bellied toad Bombina variegata suffered strong declines throughout western and northwestern parts of its range and is therefore listed as highly endangered for Germany and the federal state of Hesse. Whether chytridiomycosis may play a role in the observed local declines of this strictly protected anuran species has never been tested. We investigated 19 Hessian yellowbellied toad populations for Bd infection rates, conducted capture-mark-recapture studies in 4 of them over 2 to 3 yr, examined survival histories of recaptured infected individuals, and tested whether multi-locus heterozygosity of individuals as well as expected heterozygosity and different environmental variables of populations affect probabilities of Bd infection. Our results show high prevalence of Bd infection in Hessian yellow-bellied toad populations, but although significant decreases in 2 populations could be observed, no causative link to Bd as the reason for this can be established. Mass mortalities or obvious signs of disease in individuals were not observed. Conversely, we show that growth of Bd-infected populations is possible under favorable habitat conditions and that most infected individuals could be recaptured with improved body indices. Neither genetic diversity nor environmental variables appeared to affect Bd infection probabilities. Hence, genetically diverse amphibian specimens and populations may not automatically be less susceptible for Bd infection.

Fragile coexistence of a global chytrid pathogen with amphibian populations is mediated by environment and demography

“…While prevalence varies between 4.5% and 32%, infection intensities are generally low [11,14,16,[20][21][22][23][24]. Nonetheless, lethal chytridiomycosis has been observed in the Apennine (continental Italy) subspecies of yellow-bellied toad, B. variegata pachypus [25].…”

“…The magnitude of Bd-induced mortality for this species in the wild seems limited [16]. While prevalence varies between 4.5% and 32%, infection intensities are generally low [11,14,16,[20][21][22][23][24].…”

“…Here, we analyse a multiple-year dataset of Bd infection dynamics and demographic data in two populations (multiple-pond systems) of B. variegata, a locally endangered amphibian species hypothesized to coexist with Bd [16]. This dataset allowed us a rare possibility to study the drivers of coexistence in the absence of obvious mortality effects at the population level.…”

Chytrid fungus infection in alpine tree frogs is associated with individual heterozygosity and population isolation but not population-genetic diversity

“…No relationship was detected between individual genetic diversity and Bd infection in European tree frogs (Hyla arborea), but greater susceptibility to indirect parasite-mediated consequences of Bd exposure was documented in genetically depauperate tadpoles (Luquet et al 2012). In yellow-bellied toads (Bombina variegata), no correlation between individual heterozygosity and Bd infection was observed (Wagner et al 2017). The opposite pattern to our finding was observed in boreal toads (Bufo boreas) (Addis et al 2015), where more heterozygous individuals were more likely to be infected with Bd.…”

“…The few studies that have investigated the genetic impacts of chytridiomycosis on amphibian populations have yielded diverse and sometimes contrasting results for genetic diversity at the individual and population levels (Addis et al 2015, Luquet et al 2012, Savage and Zamudio 2011, Wagner et al 2017. For example, in lowland leopard frogs (Lithobates yavapaiensis) higher heterozygosity is associated with lower risk of Bd-associated mortality (Savage et al 2015).…”